Wide modulation bandwidth radio frequency circuit

ABSTRACT

A wide modulation bandwidth radio frequency (RF) circuit is provided. In examples discussed herein, the RF front-end circuit includes a tracker circuit configured to generate a modulated voltage at a wide modulation bandwidth. The modulated voltage can be used by an amplifier circuit(s) for amplifying an RF signal(s). Notably, the tracker circuit may have inherent frequency-dependent impedance that can interact with a load current of the amplifier circuit(s) to cause degradation in the modulated voltage, which can further lead to distortions in an RF offset spectrum. In this regard, a notch circuit is provided and configured to operate at an appropriate notch frequency and a notch bandwidth to filter the modulated voltage in the RF offset spectrum. As a result, it may be possible to reduce the distortions caused by the modulated voltage degradation in the RF offset spectrum, thus helping to improve linearity and efficiency of the amplifier circuit(s).

RELATED APPLICATIONS

This application claims the benefit of provisional patent applicationSer. No. 62/626,950, filed Feb. 6, 2018, the disclosure of which ishereby incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The technology of the disclosure relates generally to radio frequency(RF) front-end circuits.

BACKGROUND

Mobile communication devices have become increasingly common in currentsociety for providing wireless communication services. The prevalence ofthese mobile communication devices is driven in part by the manyfunctions that are now enabled on such devices. Increased processingcapabilities in such devices means that mobile communication deviceshave evolved from being pure communication tools into sophisticatedmobile multimedia centers that enable enhanced user experiences.

The redefined user experience requires a higher data rate offered bywireless communication technologies, such as fifth generation new radio(5G-NR) and Wi-Fi that typically operates in higher frequency spectrums.To achieve higher data rates with increased robustness in the higherfrequency spectrums, sophisticated power amplifiers (PAs) may beemployed to increase output power of radio frequency (RF) signals (e.g.,maintaining sufficient energy per bit) prior to transmitting the RFsignals.

Envelope tracking (ET) is a power management technology designed toimprove efficiency levels of the PAs to help reduce power dissipation inthe mobile communication devices. As the name suggests, an ET circuit isconfigured to generate a modulated voltage that keeps track of a targetvoltage envelope and provide the modulated voltage to the PAs foramplifying the RF signal(s). However, the ET circuit has inherent outputimpedance that can interact with an inherent load of the PAs,particularly at a higher modulation bandwidth (e.g., >100 MHz).Consequently, the modulated voltage may be degraded, thus leading todistortions being created outside the modulation bandwidth. As such, itmay be desirable to control the output impedance of the ET circuit tohelp reduce the distortions associated with the higher modulationbandwidth.

SUMMARY

Embodiments of the disclosure relate to a wide modulation bandwidthradio frequency (RF) circuit. In examples discussed herein, the RFfront-end circuit includes a tracker circuit configured to generate amodulated voltage (e.g., an envelope tracking modulated voltage) at awide modulation bandwidth (e.g., up to 160 MHz). The modulated voltagecan be used by an amplifier circuit(s) for amplifying an RF signal(s).Notably, the tracker circuit may have inherent frequency-dependentimpedance that can interact with a load current of the amplifiercircuit(s) to cause degradation in the modulated voltage, which canfurther lead to distortions in an RF offset spectrum. In this regard, anotch circuit is provided and configured to operate at an appropriatenotch frequency and notch bandwidth to filter the modulated voltage inthe RF offset spectrum. As a result, it may be possible to reduce thedistortions caused by the modulated voltage degradation in the RF offsetspectrum, thus helping to improve linearity and efficiency of theamplifier circuit(s).

In one aspect, a wide modulation bandwidth RF circuit is provided. Thewide modulation bandwidth RF circuit includes a tracker circuitcomprising a tracker output and configured to generate a modulatedvoltage at the tracker output. The wide modulation bandwidth RF circuitalso includes an amplifier circuit coupled to the tracker output andconfigured to amplify an RF transmit signal based on the modulatedvoltage for transmission in a time division duplex (TDD) RF spectrum.The wide modulation bandwidth RF circuit also includes a notch circuitcoupled between the tracker output and a ground, the notch circuit isconfigured to filter the modulated voltage in an RF offset spectrumadjacent to the TDD RF spectrum. The wide modulation bandwidth RFcircuit also includes a control circuit. The control circuit isconfigured to adjust a notch frequency of the notch circuit to cause thenotch frequency to fall in the RF offset spectrum. The control circuitis also configured to adjust a notch bandwidth of the notch circuit tocause the notch bandwidth to overlap with at least a portion of the RFoffset spectrum.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1A is a schematic diagram of an exemplary existing radio frequency(RF) circuit in which an amplifier circuit is configured to amplify anRF signal based on a modulated voltage generated by a tracker circuit;

FIG. 1B is a schematic diagram providing an exemplary illustration of anoutput stage of tracker circuitry in the existing RF circuit of FIG. 1A;

FIG. 1C is a schematic diagram showing that an output impedance of thetracker circuit of FIG. 1A can be modeled by an output inductance and anoutput resistance;

FIG. 1D is a schematic diagram providing an exemplary illustration of atime division duplex (TDD) RF spectrum and adjacent RF offset spectrums;

FIG. 2 is a schematic diagram of an exemplary wide modulation bandwidthRF circuit configured to filter a modulated voltage to help reducedistortions in the RF offset spectrums of FIG. 1D;

FIG. 3A is a schematic diagram of an exemplary notch circuit configuredaccording to one embodiment of the present disclosure;

FIG. 3B is a schematic diagram of an exemplary notch circuit configuredaccording to another embodiment of the present disclosure;

FIG. 4 is a graphic diagram providing an exemplary illustration offrequency-dependent output impedance before and after employing a notchcircuit in the wide modulation bandwidth RF circuit of FIG. 2;

FIG. 5 is a schematic diagram of an exemplary wide modulation bandwidthRF circuit configured to support TDD and frequency division duplex (FDD)transmissions;

FIG. 6A is a schematic diagram illustrating an exemplary configurationof a notch circuit and an RF trap in the wide modulation bandwidth RFcircuit of FIG. 5 according to one embodiment of the present disclosure;and

FIG. 6B is a schematic diagram illustrating an exemplary configurationof a notch circuit and an RF trap in the wide modulation bandwidth RFcircuit of FIG. 5 according to another embodiment of the presentdisclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region, orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present.Likewise, it will be understood that when an element such as a layer,region, or substrate is referred to as being “over” or extending “over”another element, it can be directly over or extend directly over theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly over” or extending“directly over” another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Embodiments of the disclosure relate to a wide modulation bandwidthradio frequency (RF) circuit. In examples discussed herein, the RFfront-end circuit includes a tracker circuit configured to generate amodulated voltage (e.g., an envelope tracking modulated voltage) at awide modulation bandwidth (e.g., up to 160 MHz). The modulated voltagecan be used by an amplifier circuit(s) for amplifying an RF signal(s).Notably, the tracker circuit may have inherent frequency-dependentimpedance that can interact with a load current of the amplifiercircuit(s) to cause degradation in the modulated voltage, which canfurther lead to distortions in an RF offset spectrum. In this regard, anotch circuit is provided and configured to operate at an appropriatenotch frequency and notch bandwidth to filter the modulated voltage inthe RF offset spectrum. As a result, it may be possible to reduce thedistortions caused by the modulated voltage degradation in the RF offsetspectrum, thus helping to improve linearity and efficiency of theamplifier circuit(s).

Before discussing the wide modulation bandwidth RF circuit of thepresent disclosure, a brief overview of an existing RF circuit is firstdiscussed with reference to FIGS. 1A-1D to help understand common issuesrelated to supporting wide bandwidth modulation in an existing RFcircuit. The discussion of specific exemplary aspects of a widemodulation bandwidth RF circuit that can overcome the common issues inthe existing RF circuit starts below with reference to FIG. 2.

In this regard, FIG. 1A is a schematic diagram of an exemplary existingRF circuit 10 in which an amplifier circuit 12 is configured to amplifyan RF signal 14 based on a modulated voltage V_(CC) generated by atracker circuit 16. The amplifier circuit 12 has a load line R_(LOAD)that induces a current I_(CC) based on the modulated voltage V_(CC)(I_(CC)=V_(CC)÷R_(LOAD)). The current I_(CC) and the modulated voltageV_(CC) enable the amplifier circuit 12 to amplify the RF signal 14 to anoutput power P_(OUT).

The tracker circuit 16 includes charge pump circuitry 18 and anamplifier 20. The charge pump circuitry 18 is coupled to a batteryvoltage V_(BAT) and configured to generate the current I_(CC), which mayinclude both a direct current and an alternating current. The amplifier20 receives a supply voltage V_(BATAMP), which can be derived from thebattery voltage V_(BAT). The amplifier 20 may receive a target voltageV_(TARGET) and generates the modulated voltage V_(CC) as an envelopetracking (ET) modulated voltage based on the target voltage V_(TARGET).

The RF signal 14 may be modulated to follow a time-variant powerenvelope that can produce a higher peak power from time to time.Accordingly, the tracker circuit 16 is required to provide the ETmodulated voltage V_(CC) and the current I_(CC) at a sufficient levelsuch that the amplifier circuit 12 can amplify the RF signal 14 to theoutput power P_(OUT) corresponding to the higher peak power of thetime-variant power envelope. For example, the RF signal 14 has a peakpower in excess of 28.5 dBm and the amplifier circuit 12 is required toamplify the RF signal 14 to a Class 2 output power in excess of 26 dBm.If the amplifier circuit 12 has 45% power amplifier efficiency (PAE) andthe ET modulated voltage V_(CC) is at 5 V, the current I_(CC) generatedby the tracker circuit 16 would need to be approximately 314.6 mA. Assuch, the amplifier 20 needs to employ an output stage large enough toproduce the required current I_(CC).

FIG. 1B is a schematic diagram providing an exemplary illustration of anoutput stage 22 of the amplifier 20 in the existing RF circuit 10 ofFIG. 1A. The output stage 22 includes a first transistor 24 and a secondtransistor 26 disposed in series. The first transistor 24 may be ap-type field-effect transistor (pFET) and the second transistor 26 maybe an n-type field-effect transistor (nFET). When the supply voltageV_(BATAMP) is applied to the output stage 22, the first transistor 24and the second transistor 26 can produce parasitic capacitance. As such,a pair of balance capacitors C₁ and C₂ may be provided in the outputstage 22 to help balance the parasitic capacitances.

As stated above, the output stage 22 needs to produce a sufficientlylarge current I_(CC) such that the amplifier circuit 12 of FIG. 1A canamplify the RF signal 14 to the output power P_(OUT) corresponding tothe higher peak power of the time-variant power envelope. In thisregard, the first transistor 24 and the second transistor 26 need to besufficiently large, which can in turn produce larger parasiticcapacitance during operation. As a result, the balance capacitors C₁ andC₂ need to be bigger so as to provide a higher balance capacitance tobalance the increased parasitic capacitance. The increased size of thefirst transistor 24, the second transistor 26, and the balancecapacitors C₁ and C₂ can lead to a larger footprint and more powerconsumption of the output stage 22. In addition, the higher balancecapacitance introduced by the balance capacitors C₁ and C₂ can reduceslew rate of the amplifier 20, which reduces voltage modulationbandwidth of the amplifier 20.

With reference back to FIG. 1A, the tracker circuit 16 includes inherentoutput impedance Z_(OUT), which can be modeled as being primarilydetermined by an output inductance L_(ZOUT) and an output resistanceR_(ZOUT), as shown in FIG. 1C. FIG. 1C is a schematic diagram showingthat the output impedance Z_(OUT) of the tracker circuit 16 of FIG. 1Acan be modeled by the output inductance L_(ZOUT) and the outputresistance R_(ZOUT). Common elements between FIGS. 1A-1C are showntherein with common element numbers and will not be re-described herein.

Impact of output impedance Z_(OUT) on the modulated output voltageV_(CC) can be expressed in equation (Eq. 1) below.

As shown in equation (Eq. 1) above, the output impedance Z_(OUT) cancause a voltage deviation between the target voltage V_(TARGET) and theET modulated voltage V_(CC), which can be worsened when the RF signal 14is modulated at a wider modulation bandwidth (e.g., up to 160 MHz). Inaddition, the output impedance Z_(OUT) can increase power dissipation inthe existing RF circuit 10. Furthermore, when capacitance of the balancecapacitors C₁ and C₂ in the output stage 22 of the tracker circuit 16increases, the output impedance Z_(OUT) can increase as well, thusreducing a slew rate of the tracker circuit 16 and causing furtherdeviation in the modulated voltage V_(CC).

The amplifier circuit 12 may be configured to amplify the RF signal 14for transmission in a time division duplex (TDD) RF spectrum 28, asshown in FIG. 1D. The TDD RF spectrum 28 is adjacent to an RF offsetspectrum 30, which can be located above or below the TDD RF spectrum 28,but not overlapping the TDD RF spectrum 28.

The RF offset spectrum 30 may include a lower offset spectrum 32L and anupper offset spectrum 32U. The lower offset spectrum 32L and the upperoffset spectrum 32U can correspond to equal or different bandwidths. Forexample, if the TDD RF spectrum 28 has a 100 MHz bandwidth, the RFoffset spectrum 30 can have a 200 MHz bandwidth divided equally ornon-equally between the lower offset spectrum 32L and the upper offsetspectrum 32U.

With reference back to FIG. 1A, the amplifier circuit 12 may act as acurrent source to the tracker circuit 16. Notably, the current I_(CC)may have a wide current spectrum, which can interact with the outputimpedance Z_(OUT) to degrade the modulated voltage V_(CC) and createsignificant energy content in the RF offset spectrum 30 as a result ofspectral regrowth. Moreover, when the RF signal 14 is modulated at awider modulation bandwidth (e.g., >100 MHz), the output impedanceZ_(OUT) tends to increase, thus further degrading the modulated voltageV_(CC) and worsening the distortions in the RF offset spectrum 30. Assuch, it may be desirable to control the output impedance Z_(OUT) tohelp reduce distortions (e.g., noise and ripple) in the RF offsetspectrum 30.

In this regard, FIG. 2 is a schematic diagram of an exemplary widemodulation bandwidth RF circuit 34 configured to filter a modulatedvoltage V_(CC) to help reduce distortions in the RF offset spectrum 30of FIG. 1D. The wide modulation bandwidth RF circuit 34 includes atracker circuit 36 configured to generate the modulated voltage V_(CC),which can be an ET modulated voltage, at a tracker output 38. The widemodulation bandwidth RF circuit 34 includes an amplifier circuit 40configured to amplify an RF signal 42 based on the modulated voltageV_(CC) for transmission in a TDD RF spectrum, such as the TDD RFspectrum 28 of FIG. 1D. In a non-limiting example, the tracker circuit36 can support a wide modulation bandwidth of up to 160 MHz.Accordingly, the amplifier circuit 40 is able to amplify the RF signal42 modulated with more than 400 resource blocks (RBs).

To help reduce the distortions in the RF offset spectrum 30, the widemodulation bandwidth RF circuit 34 includes a notch circuit 44 coupledbetween the tracker output 38 and a ground 46. As discussed in detailbelow, the notch circuit 44 can be configured to operate at a notchfrequency located inside the RF offset spectrum 30 and with a notchbandwidth overlapping with at least a portion of the RF offset spectrum30. In a non-limiting example, the notch circuit 44 can function as abandpass or a bandstop filter to filter the modulated voltage V_(CC) inthe RF offset spectrum 30. As a result, it may be possible to reduce thedistortions caused by the modulated voltage degradation in the RF offsetspectrum 30, thus helping to improve linearity and efficiency of theamplifier circuit 40.

The notch circuit 44 may be controlled by a control circuit 48, whichcan be a microprocessor, a microcontroller, or a field-programmable gatearray (FPGA), for example. The control circuit 48 can configure thenotch circuit 44 to operate at the notch frequency and the notchbandwidth to filter the modulated voltage V_(CC) in the RF offsetspectrum 30. Like the tracker circuit 16 of FIG. 1A, the tracker circuit36 can present the frequency-dependent output impedance ZOUT to theamplifier circuit 40. In this regard, the control circuit 48 configuresthe notch circuit 44 to reduce the frequency-dependent output impedanceZ_(OUT) to help suppress spectral regrowth in the RF offset spectrum 30.

As previously discussed in FIG. 1D, the RF offset spectrum 30 mayinclude the lower offset spectrum 32L and the upper offset spectrum 32U.In this regard, in case the lower offset spectrum 32L and the upperoffset spectrum 32U correspond to different bandwidths, the controlcircuit 48 may configure the notch circuit 44 to operate at the notchfrequency between the lower offset spectrum 32L and the upper offsetspectrum 32U. In case the lower offset spectrum 32L and the upper offsetspectrum 32U correspond to equal bandwidths, the control circuit 48 mayconfigure the notch circuit 44 to operate at the notch frequency in amiddle of the RF offset spectrum 30. In either case, the control circuit48 can further configure the notch circuit 44 to operate at the notchbandwidth overlapping with at least a portion of the lower offsetspectrum 32L and at least a portion of the upper offset spectrum 32U.

In a non-limiting example, the notch circuit 44 can be aresistor-inductor-capacitor (RLC) circuit configured according toembodiments discussed next with reference to FIGS. 3A and 3B. Commonelements between FIGS. 2, 3A, and 3B are shown therein with commonelement numbers and will not be re-described herein.

FIG. 3A is a schematic diagram of an exemplary notch circuit 44A, whichcan be provided as the notch circuit 44 in the wide modulation bandwidthRF circuit 34 of FIG. 2, configured according to one embodiment of thepresent disclosure. The notch circuit 44A includes a notch output 50that is coupled to the tracker output 38. The notch circuit 44A includesfirst circuitry 52 and second circuitry 54. The first circuitry 52 iscoupled to the notch output 50. The second circuitry 54 is coupledbetween the first circuitry 52 and the ground 46. In a non-limitingexample, the second circuitry 54 can be integrated with the trackercircuit 36, while the first circuitry 52 is provided outside the trackercircuit 36 (e.g., on a printed circuit board).

The first circuitry 52 may be implemented as inductor-capacitor (LC)circuitry, which can be configured by the control circuit 48 todetermine the notch frequency. In this regard, the first circuitry 52can be configured to include an inductor 56 and at least threecapacitors 58A, 58B, 58C. The capacitors 58A, 58B, 58C are coupled inparallel between the inductor 56 and at least three coupling points 60A,60B, 60C, respectively.

The second circuitry 54 may be implemented as resistor circuitry, whichcan be configured by the control circuit 48 to set a quality point(Q-point) of the notch circuit 44 for determining the notch bandwidth.In this regard, the second circuitry 54 can be configured to include atleast three resistors 62A, 62B, 62C and at least three switches 64A,64B, 64C. The resistors 62A, 62B, and 62C are coupled in parallelbetween the coupling points 60A, 60B, 60C and the switches 64A, 64B,64C, respectively. The switches 64A, 64B, 64C are configured to couplethe resistors 62A, 62B, 62C, respectively, to the ground 46.

The control circuit 48 can selectively control (close) one or more ofthe switches 64A, 64B, 64C to set different notch frequencies anddifferent notch bandwidths for the notch circuit 44A. For example, thecontrol circuit 48 may close the switch 64A, while keeping the switches64B, 64C open, to set the notch bandwidth based on the resistor 62A andto set the notch frequency based on the capacitor 58A and the inductor56. The control circuit 48 may close the switches 64A, 64B while keepingthe switch 64C open. Accordingly, the notch bandwidth will be set basedon the resistors 62A, 62B and the notch frequency will be set based onthe capacitors 58A, 58B and the inductor 56. In this regard, byselectively closing and opening the switches 64A, 64B, 64C, the notchcircuit 44A can be configured to operate at eight (8) different notchfrequencies and 8 different notch bandwidths.

The number of switches, resistors, and capacitors employed in the notchcircuit 44A can be determined based on intended resolution with respectto the notch frequency and the notch bandwidth. For example, the notchcircuit 44A can be configured to include four (4) switches, 4 resistors,and 4 capacitors to support sixteen (16) different notch frequencies and16 different notch bandwidths. In this regard, the notch circuitdiscussed with reference to FIG. 3A is merely one of many possibleconfigurations and should by no means be considered as being limiting.

FIG. 3B is a schematic diagram of an exemplary notch circuit 44B, whichcan be provided as the notch circuit 44 in the wide modulation bandwidthRF circuit 34 of FIG. 2, configured according to another embodiment ofthe present disclosure. The notch circuit 44B includes first circuitry66 and second circuitry 68. The first circuitry 66, which can be an LCcircuit, includes an adjustable capacitor 70 and the inductor 56. Theadjustable capacitor 70 and the inductor 56 are coupled in seriesbetween a coupling point 72 and the notch output 50. The secondcircuitry 68 includes an adjustable resistor 74 provided between thecoupling point 72 and the ground 46. Accordingly, the control circuit 48can control the adjustable resistor 74 to set different Q-points fordetermining different notch bandwidths. The control circuit 48 cancontrol the adjustable capacitor 70 to set different notch frequenciesfor the notch circuit 44B.

Simulation results show that, by employing the notch circuit 44 in thewide modulation bandwidth RF circuit 34, it is possible to reduce thefrequency-dependent output impedance Z_(OUT) of the tracker circuit 36and thus reduce the distortions in the RF offset spectrum 30. In thisregard, FIG. 4 is a graphic diagram 76 providing an exemplaryillustration of the frequency-dependent output impedance Z_(OUT) beforeand after employing the notch circuit 44 in the wide modulationbandwidth RF circuit 34 of FIG. 2.

The graphic diagram 76 includes a pre-notching curve 78 illustrating afrequency response of the frequency-dependent output impedance Z_(OUT)without employing the notch circuit 44 in the wide modulation bandwidthRF circuit 34. The graphic diagram 76 includes a first post-notchingcurve 80, a second post-notching curve 82, and a third post-notchingcurve 84 illustrating respective frequency responses of thefrequency-dependent output impedance Z_(OUT) after employing the notchcircuit 44 in the wide modulation bandwidth RF circuit 34.

The first post-notching curve 80 represents the frequency response ofthe frequency-dependent output impedance Z_(OUT) when the notch circuit44 is configured with 20 nH inductance, 20 pF capacitance, and 30resistance. The second post-notching curve 82 represents the frequencyresponse of the frequency-dependent output impedance Z_(OUT) when thenotch circuit 44 is configured with 20 nH inductance, 20 pF capacitance,and 60 resistance.

The third post-notching curve 84 represents the frequency response ofthe frequency-dependent output impedance Z_(OUT) when the notch circuit44 is configured with 10 nH inductance, 40 pF capacitance, and 60resistance. As such, the combination of 10 nH inductance and 40 pFcapacitance causes the notch circuit 44 to operate at the notchfrequency of approximately 252 MHz. Simulation results show that thenotch circuit 44 can reduce spectrum distortion by approximately 10 dB.

With reference back to FIG. 2, the tracker circuit 36 includes anamplifier 86 coupled to the tracker output 38 via an offset capacitor88. The amplifier 86 is configured to generate an output voltage V′_(CC)based on a supply voltage V_(BATAMP). The offset capacitor 88 isconfigured to raise the output voltage V′cc to the modulated voltageV_(CC). The amplifier 86 can be configured to receive a target voltageV_(TARGET) having a time-variant target voltage envelope and generate anET modulated output voltage V′_(CC) corresponding to a time-variantvoltage envelope tracking the time-variant target voltage envelope.Accordingly, the offset capacitor 88 raises the ET modulated outputvoltage V′_(CC) to generate the ET modulated voltage V_(CC).

The tracker circuit 36 includes a micro inductor-based buck-boost (μLBB)circuit 90 configured to provide the supply voltage V_(BATAMP) to theamplifier 86. In a non-limiting example, the supply voltage V_(BATAMP)can be a constant voltage. The tracker circuit 36 also includes a chargepump 92 configured to generate a current I_(CC) at the tracker output 38based on a battery voltage V_(BAT). The current I_(CC) can be a directcurrent, an alternating current, or a combination of both. The currentI_(CC) and the modulated voltage V_(CC) cause the amplifier circuit 40to amplify the RF signal 42 to a desired power level.

Notably, the notch circuit 44 may introduce a delay in a respectivefrequency response in the TDD RF spectrum 28 of FIG. 1D. Accordingly,the tracker circuit 36 can include a frequency equalizer 94 tocompensate the delay introduced by the notch circuit 44. The frequencyequalizer 94 may be either a digital frequency equalizer or an analogfrequency equalizer.

The wide modulation bandwidth RF circuit 34 may be adapted to support asecond amplifier circuit configured amplify a second RF signal fortransmission in a frequency division duplex (FDD) RF transmit spectrum.In this regard, FIG. 5 is a schematic diagram of an exemplary widemodulation bandwidth RF circuit 34A configured to support TDD and FDDtransmissions according to one embodiment of the present disclosure.Common elements between FIGS. 2 and 5 are shown therein with commonelement numbers and will not be re-described herein.

The wide modulation bandwidth RF circuit 34A includes a second amplifiercircuit 96 configured to amplify a second RF signal 98 based on themodulated voltage V_(CC) for transmission in an FDD RF transmitspectrum. The wide modulation bandwidth RF circuit 34 includes a trackercircuit 36A. The tracker circuit 36A includes an RF trap 100 coupledbetween the tracker output 38 and the ground 46. The RF trap 100 isconfigured to filter the modulated voltage V_(CC) in an FDD RF receivespectrum that does not overlap with the FDD RF transmit spectrum. For amore detailed description of the RF trap 100, please refer to U.S. Pat.No. 9,298,198 B2.

The tracker circuit 36A further includes a notch circuit 44A, which isfunctionally equivalent to the notch circuit 44 of FIG. 2. The notchcircuit 44A and the RF trap 100 can be configured according to a numberof configurations. In this regard, FIG. 6A is a schematic diagram ofillustrating an exemplary configuration of the notch circuit 44A and theRF trap 100 of FIG. 5 according to one embodiment of the presentdisclosure. Common elements between FIGS. 5 and 6A are shown thereinwith common element numbers and will not be re-described herein.

In a non-limiting example, the RF trap 100 includes a second inductor102 coupled between the tracker output 38 and a first coupling node 104.The RF trap 100 also includes at least one second capacitor 106 coupledbetween at least one second coupling node 108 and the first couplingnode 104. The second coupling node 108 is coupled to the ground 46 viaat least one switch 109. In this regard, the RF trap 100 represents aninductor-capacitor (LC) circuit, which differs from the notch circuit 44of FIGS. 2, 3A, and 3B.

Continuing with the non-limiting example, the notch circuit 44A includesan adjustable capacitor 110 and an adjustable resistor 112 coupled inseries between the notch output 50 and the ground 46. The notch output50 is coupled to the second coupling node 108 of the RF trap 100. As aresult, the notch circuit 44A can eliminate the inductor 56 in FIGS. 3Aand 3B.

FIG. 6B is a schematic diagram illustrating an exemplary configurationof the notch circuit 44A and the RF trap 100 of FIG. 5 according toanother embodiment of the present disclosure. Common elements betweenFIGS. 5, 6A, and 6B are shown therein with common element numbers andwill not be re-described herein. As shown in FIG. 6B, the notch output50 of the notch circuit 44A is coupled to the first coupling node 104.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A wide modulation bandwidth radio frequency (RF) circuit comprising: a tracker circuit comprising a tracker output and configured to generate a modulated voltage at the tracker output; an amplifier circuit coupled to the tracker output and configured to amplify an RF transmit signal based on the modulated voltage for transmission in a time division duplex (TDD) RF spectrum; a notch circuit coupled between the tracker output and a ground, the notch circuit configured to filter the modulated voltage in an RF offset spectrum adjacent to the TDD RF spectrum; and a control circuit configured to: adjust a notch frequency of the notch circuit to cause the notch frequency to fall in the RF offset spectrum; and adjust a notch bandwidth of the notch circuit to cause the notch bandwidth to overlap with at least a portion of the RF offset spectrum.
 2. The wide modulation bandwidth RF circuit of claim 1 wherein: the tracker circuit has a frequency-dependent output impedance; and the notch circuit is further configured to reduce the frequency-dependent output impedance in the RF offset spectrum.
 3. The wide modulation bandwidth RF circuit of claim 1 wherein: the RF offset spectrum comprises a lower offset spectrum and an upper offset spectrum different from the lower offset spectrum; and the control circuit is further configured to: adjust the notch frequency of the notch circuit to cause the notch frequency to fall between the lower offset spectrum and the upper offset spectrum; and adjust the notch bandwidth of the notch circuit to cause the notch bandwidth to overlap with at least a portion of the lower offset spectrum and at least a portion of the upper offset spectrum.
 4. The wide modulation bandwidth RF circuit of claim 1 wherein: the RF offset spectrum comprises a lower offset spectrum and an upper offset spectrum that is identical to the lower offset spectrum; and the control circuit is further configured to: adjust the notch frequency of the notch circuit to cause the notch frequency to fall in a middle of the RF offset spectrum; and adjust the notch bandwidth of the notch circuit to cause the notch bandwidth to overlap with at least a portion of the lower offset spectrum and at least a portion of the upper offset spectrum.
 5. The wide modulation bandwidth RF circuit of claim 1 wherein: the tracker circuit is further configured to generate an envelope tracking (ET) modulated voltage at the tracker output; and the amplifier circuit is further configured to amplify the RF transmit signal based on the ET modulated voltage.
 6. The wide modulation bandwidth RF circuit of claim 1 wherein the notch circuit comprises: a notch output coupled to the tracker output; first circuitry coupled to the notch output and configured to determine the notch frequency; and second circuitry coupled between the first circuitry and the ground, the second circuitry configured to determine the notch bandwidth.
 7. The wide modulation bandwidth RF circuit of claim 6 wherein the second circuitry is integrated with the tracker circuit.
 8. The wide modulation bandwidth RF circuit of claim 6 wherein: the first circuitry comprises: an inductor coupled to the notch output; and at least three capacitors coupled in parallel to the inductor; and the second circuitry comprises: at least three resistors coupled in parallel to the at least three capacitors, respectively; and at least three switches coupled in parallel between the at least three resistors, respectively, and the ground.
 9. The wide modulation bandwidth RF circuit of claim 8 wherein the control circuit is further configured to selectively control the at least three switches to configure the notch circuit to operate in at least eight notch frequencies and at least eight notch bandwidths.
 10. The wide modulation bandwidth RF circuit of claim 6 wherein: the first circuitry comprises an inductor coupled to the notch output and an adjustable capacitor coupled to the inductor; and the second circuitry comprises an adjustable resistor coupled between the adjustable capacitor and the ground.
 11. The wide modulation bandwidth RF circuit of claim 10 wherein the control circuit is further configured to: control the adjustable capacitor to determine the notch frequency; and control the adjustable resistor to determine the notch bandwidth.
 12. The wide modulation bandwidth RF circuit of claim 6 further comprising: a second amplifier circuit configured to amplify a second RF signal based on the modulated voltage for transmission in a frequency division duplex (FDD) RF transmit spectrum; and an RF trap coupled between the tracker output and the ground, the RF trap configured to filter the modulated voltage in an FDD RF receive spectrum non-overlapping with the FDD RF transmit spectrum.
 13. The wide modulation bandwidth RF circuit of claim 12 wherein the RF trap comprises: a second inductor coupled between the tracker output and a first coupling node; and at least one second capacitor coupled between at least one second coupling node and the first coupling node.
 14. The wide modulation bandwidth RF circuit of claim 13 wherein: the first circuitry comprises an adjustable capacitor coupled to the notch output; and the second circuitry comprises an adjustable resistor coupled between the adjustable capacitor and the ground.
 15. The wide modulation bandwidth RF circuit of claim 14 wherein the notch output of the notch circuit is coupled to the at least one second coupling node.
 16. The wide modulation bandwidth RF circuit of claim 14 wherein the notch output of the notch circuit is coupled to the first coupling node.
 17. The wide modulation bandwidth RF circuit of claim 1 wherein the tracker circuit comprises: an amplifier coupled to the tracker output and configured to generate the modulated voltage at the tracker output based on a supply voltage; and a charge pump coupled to the tracker output and configured to generate a current at the tracker output.
 18. The wide modulation bandwidth RF circuit of claim 17 wherein the tracker circuit further comprises a micro inductor-based buck-boost circuit configured to provide the supply voltage to the amplifier.
 19. The wide modulation bandwidth RF circuit of claim 17 wherein the tracker circuit further comprises an offset capacitor configured to couple the amplifier to the tracker output.
 20. The wide modulation bandwidth RF circuit of claim 17 wherein the amplifier circuit is coupled to a frequency equalizer configured to compensate for a delay caused by the notch circuit. 